Different ways are known of generating a frequency shift in an optical signal. One way of doing this by using an integrated optic acousto-optical tunable filter or AOTF. Such a device uses the acousto-optic effect in a special material, such as Lithium Niobate, to generate an optical frequency shift. A surface acoustic wave transducer is fed by a driving signal, e.g. 210 MHz.
Other ways of creating frequency shifts are desirable.
The present application teaches an optical signal shifter, formed using two oscillator waveforms that are 180 degrees out of phase. The optical signal is switched between the two waveforms such that each phase modulator is used during its ascending. Hence, the waveform is shifted in the same direction by continually phase shifting between the two driving devices.